Well drilling method and apparatus

ABSTRACT

Method and apparatus for use in well drilling, such as well completion and reworking, characterized by a foam generator disposed adjacent the bit on the lower end of a drill string to which the foam making materials are delivered for forming foam adjacent the drill bit under controlled differential pressure between the drill pipe fluid column and surrounding drill pipe annulus. In one modification the foam making materials are delivered to the upper end of the drill string for flow to the lower end thereof without combining to form foam. In another modification they may be delivered through pipes directly to the lower end of the drill string. In either modification the foam making materials are discharged at high velocity and pressure conditions are maintained to prevent migration of the foam into the surrounding fluid producing formation which will usually be at relatively low back pressure.

United States Patent Jackson June 17, 1975 [54] WELL DRILLING METHOD AND3,l35.227 5/1965 Nelson l75/243 3,268,0l7 8/1966 Yarbrough l75/2l5 XAPPARATUS 3,596,720 8/l97l Elenburg l75/2l5 X [75] Inventor: John G.Jackson. uro C o. 3,605,913 9/1971 Lehtinenl... 175/69 x Assignee: LeonDu Charme Dem/gr, Coio. a 3,773,l l0 ll/l973 Groves 1. 166/309 partmteres Primary Examiner-David H. Brown [22] 0 Filed: Jan. 14, 1974Attorney, Agent, or Firm-Sheridan, Ross & Fields [2l] Appl. No.: 432,817[57] ABSTRACT Method and apparatus for use in well drilling, such as[52] U.S. Cl. 175/69; l75/2l5; l75/243', we" completion and reworking,characterized by 3 175/317; 166/309 foam generator disposed adjacent thebit on the lower [5 Int. Cl v end of a string to the foam making male i-Field Of Se h 5/69, 2, 2l5, 218, 232, als are delivered for forming foamadjacent the drill 175/236, 243, 3l7, 318, 56, 309, 205, 324; bit undercontrolled differential pressure between the 166/309, drill pipe fluidcolumn and surrounding drill pipe annulus. In one modification the foammaking materials References Cited are delivered to the upper end of thedrill string for UNITED STATES PATENTS flow to the lower end thereofwithout combining to 1,801,788 4/1931 Zublin 1. 175/205 x fflrmfoamaflothetmodificatifln y y be deliv- 2,168,1l6 8/!939 Critesetal,l66/309 d' hr ugh p pe irectly to the lower end of the 2,329,225 9/1943Snyder etal [75/324 X drill string. In either modification the foammaking 2,374,922 5/1945 Byrd 1 6/3 l1 materials are discharged at highvelocity and pressure 1 3 10957 Jacks 1775/232 X conditions aremaintained to prevent migration of the S igsg i foam into thesurrounding fluid producing formation ar e a 4 3.094.175 (W963 Jacksonlllllllllllll h 75/324 x wlnch will usually be at relatively low backpressure. 3,130,798 4/1964 Schramm ct al .4 175/69 9 Claims, 3 DrawingFigures WELL DRILLING METHOD AND APPARATUS BACKGROUND OF THE INVENTIONIn the drilling of wells for extracting fluids contained in sub-soilformations, it has long been the practice to flow a fluid downwardlythrough a tubular drill string for delivery to a drill bit at the lowerend thereof and return same to the surface through the surroundingannulus, the returning fluid carrying cuttings, sand, or other debris.Originally, drilling mud was employed for this purpose; later, air athigh velocity was employed; and more recently, foams have been employedvEach type of fluid, often referred to as the circulating fluid, has itsadvantages, the selection of which depends upon various conditions in oradjacent the well bore. In the completion of a well bore or thereworking ofa producing well, the production of which has been depleted,the principal problem is the removal of accumulated sand in the wellbore which reduces the flow rate from the surrounding formationcontaining the fluid desired to be extracted therefrom. When thepressure in the surrounding formation is only slightly above pressure inthe well bore, this presents further problems. For example, if the fluidpressure of the circulating liquid exceeds the formation fluid pressure,the circulating fluid may flow into the formation and reduce itspermeability, thus reducing the rate of flow of the desired extractedfluid therethrough. Thus, ideally, a pressure drop between the formationand well bore is desirable to obviate outward flow of the circulatingfluid into the formation. This, of course, means that the staticpressure at the lower end of the annular column surround ing the drillstring must be less than the fluid static pressure within the formation.If the well is relatively deep and the formation fluid pressure is lessthan the static head of the fluid columns within the drill string or thesurrounding recirculating column, it becomes apparent that outward flowof the circulating fluid into the formation is inevitable.

While the use of foam as a circulating medium has been employed, which,of course, reduces the static heads in the columns just referred to,there has been no control of the foam pressure in the locus of the drillbit and surrounding pressure. Generally, the foam is formed at theground surface above the well and pumped into the drill string.

SUMMARY OF THE INVENTION In the present invention, foam is employed asthe circulating medium, generally as heretofore, but with the essentialdifference that the drill string contains the mixed ingredients forproducing foam which are discharged at high velocity in the locus of thedrill bit. The pressure at the point of discharge equals the static headof the column within the drill string (plus any pressure applied at theupper end thereof) which pressure is not applied to the formation. Thestatic pressure of the foam formed adjacent the drill bit and deliveredthereto is preferably controlled such that it, together with the statichead of the recirculated annular foam column, is less than formationstatic pressure so that fluid flow from the formation is toward the wellbore, thus preventing any outward circulating fluid flow into theformation tending to reduce its permeability.

The foam forming apparatus comprises a tubular member havingconventional drill pipe connections at the ends thereof, one of whichmay be secured to a drill bit and the other to the lower end of a drillpipe string. An adjustable spring loaded valve is provided to controlthe flow of the foam forming materials in the drill pipe to the drillbit in accordance with a desired pres sure drop therebetween. Adischarge jet operates at sufficiently high velocity and tubulence toproduce the desired foam. The control valve and discharge jet arepreferably formed within an insert which may be dropped into the tubularmember or removed therefrom without removing the drill string from thewell bore.

One of the objects, accordingly, is to provide apparatus for use with awell drill string for generating foam adjacent a drill bit from a supplyof foam generating materials contained within the drill string above theapparatus.

Another object is to control the pressure drop between the supply andthe generated foam.

Another object is to control the pressure drop so that the foam pressureis less than the static pressure of fluid in a surrounding fluid-bearingformation.

Another object is to discharge the foam generating materials through ajet at high velocity and produce turbulence of the jet to form the foam.

Another object is to render the apparatus removable from the drillstring without removing the drill string from the well bore.

A further object is to provide a novel method for completing orreworking a well bore with the use of a foam circulating medium.

Still further objects, advantages, and salient features will become moreapparent from the detailed description to follow, the appended claims,and the accompanying drawing to now be briefly described.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a central section through thelower end of a drill string and surrounding casing with the subject ofthe invention disposed between the lower end of the drill string and thedrilling bit;

FIG. 2 is a section taken on line 22, FIG. 1', and

FIG. 3 is a section taken on line 3-3, FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to thedrawing, and first to FIG. I, casing 10 may be assumed to be theexisting casing of a well, the production of which has been depleted dueto clogging or partial clogging by said or other debris which hasentered same from the surrounding formation, removal of which is desiredto restore productivity. The clogging material may have entered throughthe lower end of the casing or through perforations therein (not shown).Drill string 12 is of conventional construction, the sections of whichare coupled by tapered threads 14, the upper end of which is rotated bya rotary table or the like (not shown) as understood in the art, anannulus l6 surrounding the drill string through which the material is tobe flowed to the surface of the earth.

The subject of the invention comprises a hollow short drill stringextension 18, the upper end of which is threadedly connected to thelower end of drill string 12, its lower end having a suitable drillingbit 20 threadedly connected thereto which may be of any conventionalconstruction and provided with a conduit 22 communicating the interiorof the extension with annulus 16. Extension 18 is provided with atapered seat 24 upon which sealingly rests foam delivery apparatus 26which contains the operative parts to now be described in detail.

Referring now to P10. 2, apparatus 26 is provided with a bore 28 whichslideably receives a piston valve 30 having apertures 32 whichcommunicate with aper tures 34 in the position shown and which move tononcommunicative position (not shown) when the piston valve movesupwardly. A valve stem 36 is affixed to the piston valve and is urgedupwardly by a spring 38 disposed between an apertured bulkhead 40 and acollar 42 which may be adjusted axially on the valve stem to provide adesired spring force. The upper end of the valve stem is provided with aconical head 44 which may receive a suitable fishing tool (not shown)which may be dropped into the drill string for engaging the conical headand removing apparatus 26 from the drill string. Bore 28 is alsoprovided with a fixed plate 46 having a rectangular aperture 48extending therethrough, also shown in FIG. 3, which delivers fluidtherethrough at high velocity for impingement on knife edge 50 affixedto a fixed apertured bulkhead 52. As will be apparent from the arrows inFIG. 2, foam making fluid is delivered downwardly through the drillstring, its static head (or additional pressure applied thereto at thesurface) being sufficient to move the piston valve against the urge ofthe spring to the position shown. The fluid then flows through apertures34,32 and 48 at which locus the fluid is flowing at high velocity forimpingement on knife edge 50, the foam pro duced then flowing throughthe drill bit and into annulus 16 for upward discharge to the surfacealong with the foreign material which is to be removed from the casing.

OPERATION General As an example of the operation of the construction sofar described, it will be assumed that a producing well, which may begas, oil, or water, is to be reworked because of production depletionresulting from said clogging of the well bore. It will also be assumedthat the fluid pressure in the surrounding formation is relatively lowwhich precludes use of a high pressure fluid in the well bore whichwould force said or other debris outward into the formation, thustending to clog same and reduce its permeability. It thus becomesapparent that the applied pressure at the bottom of the bore should beless than formation fluid pressure. Now, if foaming ingredients, such aswater, air and a foaming agent, were mixed at the surface to form foamand introduced into the upper end of the drill string, the static headof the foam column could well be less than the formation fluid pressure,thus requiring pumping pressure to be added at the top of the foamcolumn. In the present invention, and in contra-distinction to theprocedure just referred to, the foaming ingredients, but in unfoamed andmore dense form, are introduced into the upper end of the drill stringand foaming occurs at the bottom of the drill string rather than at thesurface. The static head of the unfoamed mixture is, of course,considerably greater than a foam column as in the prior art. This statichead will often be sufficient for producing the foam and desiredpressure differential at the bottom of the well bore, but if not, only arelatively small pressure need be added to the unfoamed mixture at thetop of the column.

Normally, the foam producing ingredients may be delivered to the upperend of the drill string as just described. In some instances, however,it may be found desirable to introduce some or all of the ingredients atthe bottom of the drill string. FIG. 2 includes this modification inwhich pipes 54,54 extend from the surface to near the lower end of thedrill string and through which some or all of the ingredients may beintroduced without flowing downwardly through the entire length of thedrill string thus minimizing some foaming which might occur therein.Ordinarily, the foaming agent would be introduced through one of thesepipes and water or air through the other, the drill string forming theconduit of the normally third ingredient. This modification, however,introduces mechanical and other complications which would normally beavoided.

Control Valve Valve 32,34 and spring 38 control the rate of discharge ofthe foam producing ingredients to the lower end of the well bore. Thespring is so chosen (or its spring pressure adjusted by collar 42) tocontrol the differential pressure between the foam producing ingredientsand foam discharge pressure at the bottom of the well bore so that thelatter is somewhat less than formation fluid pressure. This, of course,prevents flow of foam or entrained debris outwardly into the formationtending to clog same.

Foam Ingredient Discharge When the foam producing ingredients aredischarged at relatively high velocity into a region of low pressurethey form a foam mixture of very low density as compared to their formerstate. Various discharge orifices may be employed but the typeillustrated is preferred, this type sometimes being known as a sonulatorwhich generates ultrasonic acoustic energy, resulting in production of afoam having improved characteristics. Such devices are well known asexemplified by those manufactured by Sonic Engineering Corporation,Norwalk, Conn.

Foam Producing Mixtures There are many foaming agents available forrendering water and other liquids foamable, some of which are noted inthe U.S. Pat. to Schramm, No. 3,130,798 and Schneider, US. Pat. No.3,313,362. Some which are available on the market are conventionaldetergents and tradesecret agents such as Triton 05-1 5" sold by Rohmand Haas Co. of Philadelphia, Pa, and *Snyfoam" sold by Swift and Co. ofChicago. An agent for stiff foam is marketed under the trade nameMagcobar, and an agent for foaming oily liquids is marketed under thetrade name AMBIDEX by Carlisle Chemical Works of Reading, Ohio. Noinvention resides in the foaming agent as most if not all of theconventional foaming agents on the market can be used.

What is claimed is:

1. ln well drilling apparatus for use in a formation having relativelylow fluid pressure, such as a debris clogged and production depletedwell, said apparatus including a drill string and a drilling bit at thelower end thereof adapted to drill a well bore of a diameter to form anannulus surrounding the drill string, the improvements, in combination,comprising:

a. a tubular member disposed adjacent the lower end of said drill stringand forming a part thereof for rotating the bit;

b. a foam generator disposed within said tubular member;

0. said generator having a normally closed control valve means soconstructed and arranged to open upon application thereto ofpredetermined pressure of a mixture supply of substantially unfoamedfoam producing ingredients, such as air. water and a foaming agent;

d. a mixture discharge orifice communicating with said valve and thelower end of said annulus; and

e. means for delivering said mixture to said valve;

f. whereby said valve is adapted to open in response to differentialpressure between mixture supply pressure and pressure at the lower endof said annulus and deliver said mixture to said orifice. said orificebeing so constructed to pass said mixture therethrough at high velocityand convert same to a foam, the foam pressure static head at the lowerend of said annulus being controlled to be insufficient for anysubstantial flow thereof into said formation but sufficient to causeupward flow thereof in said annulus to thereby carry debris cut by saidbit to the upper end of said annulus for discharge therefrom.

2. Apparatus in accordance with claim 1 wherein the means for deliveringsaid mixture to said valve means consists of the drill string bore.

3. Apparatus in accordance with claim I wherein the means for deliveringsaid mixture to said valve means includes at least one conduit withinthe drill string bore extending from the surface to near the lower endthereof.

4. Apparatus in accordance with claim I wherein said control valve meanscomprises a hollow piston slideable within a bore and having ports inthe wall thereof adapted to communicate with ports in the wall of thebore, a valve stem affixed to the head of the piston, a spring forurging the valve stem toward valve closed position, and a head on thevalve stem adapted to be grasped by a fishing tool for removing thevalve means through the bore of the drill string.

5. Apparatus in accordance with claim 1 wherein said mixture dischargeorifice is rectangular in cross section and discharges the mixture ontoa knife edge at ultrasonic velocity to affect ultra-sonic vibrations andcavitation within the liquid and produce small stable gas bubblestherein.

6. Apparatus in accordance with claim 1 wherein said tubular member isconstructed as a relatively short drill string extension havingconventional couplings at the ends thereof for connection to the drillstring and the drill bit.

7. Apparatus in accordance with claim 6 wherein said foam generator isso constructed to sealingly engage the tubular member by mutuallycooperating surfaces against unauthorized mixture flow to the annulus,said generator being removable through the drill string without removingsame from the well bore.

8. Method of drillling or reworking a well having a bore extending intoa formation having relatively low fluid pressure and containing debris,such as sand, which it is desired to remove with a circulating foam,comprising the steps of:

a. drilling into said debris with a conventional hollow rotatable drillstring having a drill bit at its lower end adapted to produce an annulussurrounding the drill string,

b. introducing foam producing ingredients, such as air, water and afoaming agent through the drill string for delivery at the lower endthererof,

c. flowing the delivered ingredients through a control valve to maintaina discharge pressure less than the surrounding formation fluid pressureto obviate flow of the debris into the formation, and

d. discharging the ingredients through an orifice adjacent the drill bitto convert the ingredients into a lighter density foam adapted to carrythe debris through said annulus to the surface.

9. A well drilling process for use in a formation having relatively lowfluid pressure, such as a debris clogged and production depleted well,and with a drill string and a drilling bit at the lower end thereofadapted to drill a well bore ofa diameter to form an annulus surrounding the drill string, comprising;

a. rotating the bit by a tubular member forming a part of the lower endof the drill string, and having a foam generator therein;

b. delivering a mixture supply of substantially unfoamed foam producingingredients, such as air, water and a foaming agent to said tubularmember under predetermined pressure;

c. delivering the mixture supply through a pressure control valve in thegenerator;

d. delivering the mixture supply from the control valve through amixture discharge orifice at high velocity to convert same to foam; and

e. delivering the foam to the lower end of said annulus at a controlledstatic pressure head insufficient for any substantial flow thereof intosaid formation but sufficient to cause upward flow thereof in saidannulus to thereby carry debris cut by said bit to the upper end of saidannulus for discharge there from.

1. In well drilling apparatus for use in a formation having relativelylow fluid pressure, such as a debris clogged and production depletedwell, said apparatus including a drill string and a drilling bit at thelower end thereof adapted to drill a well bore of a diameter to form anannulus surrounding the drill string, the improvements, in combination,comprising: a. a tubular member disposed adjacent the lower end of saiddrill string and forming a part thereof for rotating the bit; b. a foamgenerator disposed within said tubular member; c. said generator havinga normally closed control valve means so constructed and arranged toopen upon application thereto of predetermined pressure of a mixturesupply of substantially unfoamed foam producing ingredients, such asair, water and a foaming agent; d. a mixture discharge orificecommunicating with said valve and the lower end of said annulus; and e.means for delivering said mixture to said valve; f. whereby said valveis adapted to open in response to differential pressure between mixturesupply pressure and pressure at the lower end of said annulus anddeliver said mixture to said orifice, said orifice being so constructedto pass said mixture therethrough at high velocitY and convert same to afoam, the foam pressure static head at the lower end of said annulusbeing controlled to be insufficient for any substantial flow thereofinto said formation but sufficient to cause upward flow thereof in saidannulus to thereby carry debris cut by said bit to the upper end of saidannulus for discharge therefrom.
 2. Apparatus in accordance with claim 1wherein the means for delivering said mixture to said valve meansconsists of the drill string bore.
 3. Apparatus in accordance with claim1 wherein the means for delivering said mixture to said valve meansincludes at least one conduit within the drill string bore extendingfrom the surface to near the lower end thereof.
 4. Apparatus inaccordance with claim 1 wherein said control valve means comprises ahollow piston slideable within a bore and having ports in the wallthereof adapted to communicate with ports in the wall of the bore, avalve stem affixed to the head of the piston, a spring for urging thevalve stem toward valve closed position, and a head on the valve stemadapted to be grasped by a fishing tool for removing the valve meansthrough the bore of the drill string.
 5. Apparatus in accordance withclaim 1 wherein said mixture discharge orifice is rectangular in crosssection and discharges the mixture onto a knife edge at ultra-sonicvelocity to affect ultra-sonic vibrations and cavitation within theliquid and produce small stable gas bubbles therein.
 6. Apparatus inaccordance with claim 1 wherein said tubular member is constructed as arelatively short drill string extension having conventional couplings atthe ends thereof for connection to the drill string and the drill bit.7. Apparatus in accordance with claim 6 wherein said foam generator isso constructed to sealingly engage the tubular member by mutuallycooperating surfaces against unauthorized mixture flow to the annulus,said generator being removable through the drill string without removingsame from the well bore.
 8. Method of drillling or reworking a wellhaving a bore extending into a formation having relatively low fluidpressure and containing debris, such as sand, which it is desired toremove with a circulating foam, comprising the steps of: a. drillinginto said debris with a conventional hollow rotatable drill stringhaving a drill bit at its lower end adapted to produce an annulussurrounding the drill string, b. introducing foam producing ingredients,such as air, water and a foaming agent through the drill string fordelivery at the lower end thererof, c. flowing the delivered ingredientsthrough a control valve to maintain a discharge pressure less than thesurrounding formation fluid pressure to obviate flow of the debris intothe formation, and d. discharging the ingredients through an orificeadjacent the drill bit to convert the ingredients into a lighter densityfoam adapted to carry the debris through said annulus to the surface. 9.A well drilling process for use in a formation having relatively lowfluid pressure, such as a debris clogged and production depleted well,and with a drill string and a drilling bit at the lower end thereofadapted to drill a well bore of a diameter to form an annulussurrounding the drill string, comprising; a. rotating the bit by atubular member forming a part of the lower end of the drill string, andhaving a foam generator therein; b. delivering a mixture supply ofsubstantially unfoamed foam producing ingredients, such as air, waterand a foaming agent to said tubular member under predetermined pressure;c. delivering the mixture supply through a pressure control valve in thegenerator; d. delivering the mixture supply from the control valvethrough a mixture discharge orifice at high velocity to convert same tofoam; and e. delivering the foam to the lower end of said annulus at acontrolled static pressure head insufficient for any substantial flowthereof into said formation but sufFicient to cause upward flow thereofin said annulus to thereby carry debris cut by said bit to the upper endof said annulus for discharge therefrom.